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Nanoscale study on water damage for different warm mix asphalt binders
Accepted Manuscript Nanoscale Study on Water Damage for Different Warm Mix Asphalt Binders Liu Kefei, Deng Linfei, Zheng Jiayu PII: DOI: Reference:
S1996-6814(16)30028-1 http://dx.doi.org/10.1016/j.ijprt.2016.11.001 IJPRT 52
To appear in:
International Journal of Pavement Research and Technology
Received Date: Accepted Date:
26 February 2016 3 November 2016
Please cite this article as: L. Kefei, D. Linfei, Z. Jiayu, Nanoscale Study on Water Damage for Different Warm Mix Asphalt Binders, International Journal of Pavement Research and Technology (2016), doi: http://dx.doi.org/ 10.1016/j.ijprt.2016.11.001
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Nanoscale Study on Water Damage for Different Warm Mix Asphalt Binders LIU Kefei1+ , DENG Linfei 1 and ZHENG Jiayu1 Abstract: In order to analyze the water damage to different warm mix asphalt binders from the the micro scale, five kinds of asphalt binders, 70#A base asphalt, sasobit warm mix asphalt, energy champion 120 （ EC120 ） warm mix asphalt, aspha-min warm mix asphalt, sulphur-extended asphalt modifier (SEAM) warm mix asphalt, under different conditions (dry/wet, original/aging) are prepared for laboratory tests. The atomic force microscope (AFM) is used to observe the surface properties and measure the adhesion force between the asphalt and the mineral aggregate. The obtained results show that under the dry condition aspha-min warm mix asphalt and SEAM warm mix asphalt show stronger adhesive ability with the mineral aggregate compared with other asphalt binders, but also have relatively large dispersion and fluctuation in the tested results; under the wet condition, aspha-min warm mix asphalt and SEAM warm mix asphalt show stronger water damage resistance ability. The EC120 warm mix asphalt and aspha-min warm mix asphalt are less sensitive to moist, and their corresponding adhesion force is less susceptible to the change of external moisture conditions, leading to a better ability to resist water erosion. The aging process significantly lowers the moisture erosion resistance ability, which further impairs the water damage resistance ability. The base asphalt is more sensitive to moisture and more vulnerable to water damage, no matter whether it is under original or aging conditions. The aging aspha-min warm mix asphalt has the least loss of adhesion force, the smallest dispersion of the tested adhesion force, the strongest water damage resistance ability, no matter it is dry or wet. Key words: Road engineering; Warm mix asphalt; Moisture damage; Atomic force microscope; Microcosmic pavement have not been solved thoroughly: 1 Introduction How to exactly measure the asphalt mixture performance loss caused by moisture variation? The material and structural characteristic of How to effectively reduce the water damage to asphalt concrete pavement make it more asphalt pavement? susceptible to the moisture condition. The Numerous studies [1-6] have showed that decrease of the adhesion force causes the the water damage of asphalt binders (mixtures) water damage at the asphalt-aggregate occurs at the molecular scale, or even at the interface. Although the domestic and overseas nanometer scale. This is because of the fact researches on water damage to asphalt that the root cause of water damage to asphalt pavement has lasted nearly 70 years, this binders is related to the loss of the adhesion problem has not yet been effectively addressed. force and the cohesion force. The loss of the Two key problems of water damage in asphalt adhesion force refers to the decline of the adhesive ability at the asphalt-aggregate 1 Associate Professor, College of Civil interface as a result of the water and water Engineering and Mechanics, Central South pressure acting on the asphalt mixture; the loss University of Forestry & Technology, of the cohesion force is due to the softening or China-410004. + the impairment of cohesion capability inside Corresponding Author: E-mail [email protected]
the asphalt binder subjected to the moisture and seepage force. Both the adhesion force loss and the cohesion force loss happen at the nanometer scale. Therefore, to quantify the adhesion force or the cohesion force at the nanometer scale is of highly positive practical significance to the research and prevention of water damage to the asphalt pavement. The microscopic researches on water damage to the asphalt binders at home and aboard mainly focus on base asphalt and SB/SBS modified asphalt. However, there are few reports about the investigation of warm mix asphalt at the nanometer scale. With the application of the high-definition 3D image resolution of the atomic force microscope (AFM) and a precise force-displacement measurement system, the adhesion force between the asphalt-aggregate molecules is analyzed for different asphalt binders under dry/wet, original/aging states at the laboratory, followed by the evaluation of the water damage resistance for each warm mix asphalt binder under different conditions. The research results can provide theoretical basis for the discovery of the mechanism of water damage and the reduction of water damage. It should be noted that parallel tests are conducted in this article using modified asphalt SBS as comparative material, and the results showed no visible difference. In consequence, this article only presented the effects of base asphalt and warm mix modifies on water damage of asphalt binder.
Review of Previous Studies Research on water damage of asphalt binder & mixture dates back to the 1930s, from asphalt to mineral aggregate, from test methodology to pavement structure[7]. To date, numerous test
methods have been developed and used to predict moisture-induced damage in asphalt concrete[8-10]. In the past two decades, there
have been significant improvements in moisture damage test methods and our understanding of the microscale to macroscale behavior of asphalt concrete. There exists evidence that moisture-induced damage in asphalt concrete is influenced by factors such as asphalt grade, viscosity, modifiers, phenol group concentrations, aggregate surface chemistry, minerals, roughness, porosity, clay coatings, mix air voids, asphalt content, permeability, and binder thickness. Yet, a combination of asphalt and aggregate that would be compatible enough to produce moisture damage-free asphalt concrete is not available[11]. There is an urgent need for the development and assessment of testing methods capable of examining the effect of moisture on asphalt concrete. Moisture damage within the binder and/or at asphalt-aggregate interfaces has been studied by several researchers[2,6,8]. Recently, the surface free energy of asphalt and aggregate has been empirically related to the moisture-induced damage of asphalt concrete[2,5]. The surface free energy of asphalt and aggregate is indirectly measured using the Wilhelmy plate, sorption device, and Youn-Dupré equation. However, the Wilhelmy plate method cannot differentiate between the functional groups. For example, the surface free method fails to differentiate between actions of carboxylic acid (bad) and carbonyls (good), or carboxylic acid (bad) and nitrogen compound (good) under wet conditions. Also, the Wilhelmy plate technique cannot clearly distinguish between untreated asphalt and asphalt treated with amine antistrip. By the same token, the universal sorption device requires vacuum degas preconditioning, which is very different from the mixing plant conditions. More recently, Rafiqul et al [12] tested the adhesion forces between base asphalt as well as SB & SBS modified asphalts and different functional probes. The results
showed that modifiers SB and SBS can improve the water damage-proof ability of base asphalt and a 3% SB & SBS dosage can obtain the best effect. In addition, critical parameters for AFM testing on modified asphalt were also confirmed basically.
Material and Test Method Raw Materials The raw materials used in the tests include: (1) The base asphalt: 70#A pavement petroleum asphalt. (2) The warm mix modifier sasobit: with low melting point and organic viscosity-reducing character. The admixture dosage is 3.0 percent of the mass of the asphalt binder, which can lower the mixed and compacted temperature by 20 ～ 30 . (3) The warm mix additive energy champion 120 (EC120): a kind of linear aliphatic hydrocarbons. The admixture dosage is 3.0 percent of the mass of the asphalt binder, lowering the mixed and compacted temperature by 20 ～30 . (4) The warm mix additive aspha-min: the artificial synthetic white powder zeolite. The admixture dosage is 0.3 percent of the mass of the asphalt binder, lowering the mixed and compacted temperature by 10 ～25 . (5) The warm mix additive sulphur-extended asphalt modifier (SEAM): the sulfur. The admixture dosage is 30 percent of the mass of the asphalt binder, lowering the mixed and compacted temperature by 20 ～35 . Each appearance of warm mix additives is shown in Figure 1, and the main technical parameters of the asphalt binders are listed in Table 1.
The Preparation of Samples In order to ensure the AFM to reliably observe the nanometer-scale surface properties of asphalt binders, the one-blending method is
used to prepare the warm mix asphalt samples which are theoretically finely dispersed and uniformly distributed. In order to make the binder surface smooth, the particle size of asphalt mortar should be as small as possible, an advanced colloid mill machine (2000 mesh) is taken to grind the warm mix asphalt fully mixing the warm agents with the asphalt, at the revolving speed 4500rpm and grinding time 4h. The detailed preparation technology is sketched in Figure 2. Moreover, size of material will not change the character of itself and the usage of colloid mill machine for asphalt binder grinding will also make no difference to the results or the engineering application. In order to compare the adhesion forces between asphalt and aggregate molecules under different conditions, according to the test code of ASTM D6521, the original and aging samples are obtained by further processed the residuary asphalts with PAV stress aging（100 ）which are left after the RTFOT（163 ） aging. The basic technical parameters for aging asphalt binders are given in Table 1. In order to prevent the further aging, firstly respectively place 20g of the prepared asphalt binders into an oven at 140 and rapidly heat to melt; then drip moderate melted binders on a glass slide and put the glass slide into an oven at 140 for five minutes to obtain a smooth surface; finally take out the sample and keep it natural cooling to room temperature.
(a) Sasobit
(b) EC120
(c) Aspha-min
(d) SEAM
Fig.1. The Appearance of Warm Mix Additives Table 1. Main Technical Indexes of Each Asphalt Binder Type of Asphalt
70#A Base Asphalt
Sasobit Warm Mix Asphalt
EC120 Warm Mix Asphalt Aspha-min Warm Mix Asphalt SEAM Warm Mix Asphalt
Original After PAV Aging Original After PAV Aging Original After PAV Aging Original After PAV Aging Original After PAV
Penetration (25℃)(0.1mm)
Penetration Index PI
Ductility (5℃)(cm)
Softening Point(℃)
76
-0.80
19
46.4
Elastic Recovery (25℃) (%) --
52
-0.68
9.8
52.4
--
56
0.37
14.8
63.5
89.1
48
0.43
11.0
73.0
82.6
59
0.46
12.7
61.7
87.4
51
0.51
9.8
68.5
81.6
61
0.39
17.9
58.2
89.6
53
0.45
12.9
64.3
83.7
63
0.40
13.5
64.1
91.0
54
0.47
8.3
70.4
82.3
Aging
Fig.2. Preparation Process Flow Chart for Warm Mix Asphalt Binder For the purpose of comparisons between force-displacement curves. The scanned the dry and wet conditions, making reference figures were further processed using the to Reference [12], the wet samples were MATLAB. Ten feature points were scanneded obtained by firstly putting the dry samples in a for each sample, and the mean value of these vacuum dryer to evacuate to full vacuum and ten points was taken as the measured adhesion then immersing them in water for 72h. We force. obtained totally 20 kinds of original/aging and dry/wet asphalt binders. The Analysis of the AFM Images Before the AFM tests, all samples were placed into an oven at 140 for 2 hours for of Asphalt Binders desiccated surfaces. The typical micrographs and stereographs for Method of AFM Tests asphalt binders are shown in Figure 3. Only The Digital Instruments-Veeco Metrology the figures of the dry samples are provided for Group AFM with image resolution 180 x 180 the sake of the space. According to the points and maximum scanning range 15µm× working principle of AFM and the 15µm is used to perform all tests at the requirement of test accuracy[13-15], the mean tapping mode. The resonance frequency of value, maximum value and root-mean-square micro-cantilever is 260 kHz. of the surface roughness for each asphalt In order to effectively simulate the binder were calculated and listed in Table 2. measurement of asphalt-aggregate adhesion As seen in Table 2, the maximum and force, the silicon nitride (Si3N4) probe is used minimum values of surface roughness RMS to get the three-dimensional images at the are, respectively, 32.46nm and 7.71nm. These asphalt binder surface and measure the measured values agree well with the advice adhesion force, under the scanning frequency for the measurement of surface roughness of of 3Hz, as Silicon is the basic elements of viscoelastic material using AFM, which verify rocks and minerals. During the experiments, the preparation of the samples and the the testing work mainly focused on, with the experimental method adopted in this article. application of the probe, the search of the feature points at the surface of samples, the scan of the image, the measurement of the
（a1）Micrograph of 70#A Base Asphalt
（a2）Stereogram of 70#A Base Asphalt
(b1) Micrograph of Sasobit Warm Mix Asphalt
(b2) Stereogram of Sasobit Warm Mix Asphalt
(c1) Micrograph of EC120 Warm Mix Asphalt
(c2) Stereogram of EC120 Warm Mix Asphalt
(d1) Micrograph of Aspha-min Warm Mix Asphalt
(d2) Stereogram of Aspha-min Warm Mix Asphalt
(e1) Micrograph of SEAM Warm Mix Asphalt
(e2) Stereogram of SEAM Warm Mix Asphalt
Fig.3. Typical Surface Images of Each Asphalt Binder (Dry Sample) Table 2. Roughness Calculation Results of Each Asphalt Binder Dry Average Maximum Root-Mean Average Type of Asphalt Value Value -Square Value (nm) (nm) (nm) (nm) Original 9.3 20.2 12.51 11.3 70#A Base After Asphalt PAV 11.7 24.3 14.77 14.6 Aging Original 9.9 19.8 13.13 12.5 Sasobit After Warm Mix PAV 12.1 17.6 15.32 14.5 Asphalt Aging Original 6.5 9.6 7.71 8.3 EC120 After Warm Mix PAV 8.9 12.1 9.54 11.2 Asphalt Aging Original 21.2 41.7 24.11 24.3 Aspha-min After Warm Mix PAV 23.7 45.9 27.86 28.9 Asphalt Aging Original 24.1 44.6 28.35 27.3 SEAM After Warm Mix PAV 28.3 48.5 29.97 30.1 Asphalt Aging
Besides, both the obtained micrographs and stereographs can visually reflect the degree of surface evenness (or surface roughness) of these samples. Among the five samples, the surface morphology of 70#A base asphalt is relatively smooth, since it has no any additives. Even though there are some slight pits in the 70#A base asphalt, their distributions are relatively uniform. Under the effect of the high-speed shearing of colloid
Wet Maximum Value (nm) 24.9
Root-Mean -Square (nm) 14.18
26.3
16.22
24.6
14.27
26.9
17.73
14.2
8.85
18.3
12.16
46.2
28.56
48.8
31.12
49.4
30.52
48.9
32.46
grinder, a uniform and stable spatial network system is generated in the sasobit warm mix asphalt or the EC120 warm mix asphalt in which several relatively large polymer particles exist, but both two kinds of warm mix additives basically disperse well among the base asphalts, the surface morphology of the binders being relatively smooth and even, which constitutes a good compatible system. The surfaces of aspha-min warm mix asphalt and SEAM warm mix asphalt are very rough
with many sags and crests under irregular distributions. The maximum height in Z-axis is about 50 nm. This indicates that the addition of warm mix additives aspha-min and SEAM into the base asphalt significantly increases the granular size and dispersion degree of the mixed particles, thus the compatibility is poorer than those of other warm mix binders[16].
The Measurement of Adhesion Force
The force-distance curves of the dry original samples for all warm mix asphalts are shown in Figure 4. The horizontal axis in Figure 4 represents the distance between the Si3 N4 probe and the sample surface, and the vertical axis represents the magnitude of the force between the probe molecule and the asphalt molecule, positive values for repulsive forces and negative values for attractive forces. Each test cycle starts at the position with a distance bigger than 500nm from the sample surface. The curves in Figure 4 show that there are four representative sections, respectively separated by points A, B, C and D.
(a) 70#A Base Asphalt
(b) Sasobit Warm Mix Asphalt
(c) EC120 Warm Mix Asphalt
(d) Aspha-min Warm Mix Asphalt
(e) SEAM Warm Mix Asphalt
Fig.4. Force-distance Test Chart of Each Asphalt Binder (Dry Sample) When the probe is far away from the sample surface (the right part at point A on the curve), there is no interaction between the probe molecule and the asphalt molecule. As the probe is approaching the sample surface, the attractive force between the probe molecule and asphalt molecule makes the
probe further move close to the sample (the AB part on the curve). This attractive force reaches its maximum value at point B beyond which point the attractive force gradually turns into the repulsive force which stops the probe approaching. The closer the probe gets to the surface of sample, the faster the
repulsive force grows (the BC part on the curve). The repulsive force reaches its peak at point C when the probe molecule gets infinitely close to the asphalt molecule. Then, the probe begins to get away from the sample surface. At the beginning, the attractive force dominates the interaction between the probe molecule and asphalt molecule, and this attractive force increases with the increase of the distance between these two molecules (the CD part on the curve), reaching the maximum value at point D. After point D, the probe molecule gets rid of the restriction of adhesion force from the asphalt molecule and slowly returns to the initial state (the DA part on the
curve). The corresponding value at point D represents the maximum adhesion force between the probe and asphalt molecules caused by the van der waals’ force [17, 18].
The Analysis of the Tested Results The Analysis of the Tested Results of Original Asphalt Binders The tested adhesion forces for original asphalt binders are given in Table 3.
Table 3.
Adhesion Force Test Results of Original Asphalt Binders Sasobit Aspha-min 70#A Base EC120 Warm Warm Mix Warm Mix Asphalt Mix Asphalt Point Asphalt Asphalt Dry Wet Dry Wet Dry Wet Dry Wet 71.3
67.5
67.9 68.5
69.4 55.6
77.4
57.9
73.5 70.1 69.0
63.1 67.3 56.6
66.4 72.2
55.8 68.3
70.8 70.7
61.5 62.3
3.82 4
2.99 6
8.85
4.24
1
103.7
71.3
49.6
38.5
2
88.9
52.5
52.7
42.7
3
111.2
47.9
58.8
46.8
4
101.5
50.7
59.1
44.3
5 6
86.5 88.2
58.5 47.8
54.3 55.6
39.6 37.2
7
107.4
46.7
56.1
45.8
8
85.3
63.4
52.5
47.5
9
91.2
67.9
58.4
40.9
10
114.1
57.3
56.9
48.7
Average (nN)
97.8
56.4
55.4
43.2
10.41 5
8.34 6
2.95 9
10.42
14.8 0
5.34
Standard Deviation(nN ) Percent Variation(%)
Combined with the previous research, the
97.9 95.4 103. 8 96.9 109. 3 119.8 105. 5
125. 4 119.6 132. 7 121. 5 118.3 119.0 125. 7 116.4 121. 0 117.5 121. 7
5.27 9
8.42 5
8.47
7.99
117.4 113.1 102. 8 98.6
SEAM Warm Mix Asphalt Dry 98.7 117.4 105.9 93.5 102.6 95.5 93.9 112.6 96.2
Wet 84.6 88.2 95.7 99.6 80.3 83.1 101. 5 87.6 92.5
103.6
83.9
110.0
89.7
4.69 3
11.10 8
6.92 3
3.86
10.10
7.72
process of water infiltration in asphalt binder
is known as follows: hydrone has a tremendous polarity, and once water contacted with the asphalt surface, the interaction between hydrones and the polar molecules or groups such as aromatic hydrocarbons, colloids and asphaltenes in asphalt will take place by orientation forces, and a micro-activating center will then formed by hydrones aggregation. Due to the directionlessness and saturability of orientation forces, the adsorbed hydrones will continue to interact with the polar groups nearby to form new micro-activating centers. Similarly, the micro-activating centers can also be formed through the induction forces between the hydrones and the nonpolar molecules & constituents, what’s more, due to the directionlessness and saturability of the induction forces, just like the orientation forces, the hydrones will also continue to interact with the nonpolar constituents nearby. In addition, the hydrones will interact with the oxygen and nitrogen atoms in asphalt to form hydrogen bonds. Capillary channels for water enrichment and infiltrate constructed by micro-activating centers are formed by the above three types of intermolecular interactions, through these channels, water enriches in the asphalt layer and expand to the mineral aggregate surface. This is how the progress of water diffusion passage formed. After it, hydrones continually get to reach the interface of the asphalt and mineral aggregates and interact with the asphalt as mentioned above. More hydrones get into the asphalt as the contact surface getting large and then the asphalt will get saturated and accommodates no hydrones any more when the interactions between hydrones and polar and nonpolar component & strong electronegativity elements were completed. In the progress, a slower capillary channels formation velocity means a smaller velocity of water diffusion, namely a greater capacity of water
damage-proof and vice versa. Based on the above analysis, conclusions from the AFM tests can be drawn: (1) the most gentle curve near point D comes from the original base asphalt in the Figure 4, which indicates that its viscosity is obviously greater than that of the warm mix asphalts. This is consistent with the previous studies. (2) For the original asphalt binders, the ranking order of the adhesion force under dry condition is: SEAM warm mix asphalt （ 110.0nN ） ＞ aspha-min warm mix asphalt（105.5nN）＞ 70#A base asphalt（97.8nN）＞EC120 warm mix asphalt（70.7nN）＞sasobit warm mix asphalt (55.4nN). This means that under the dry condition the aspha-min warm mix asphalt and SEAM warm mix asphalt have better adhesion to the mineral aggregate than that of other asphalt binders. (3) Under the dry condition, the standard deviation of the tested adhesion force for original base asphalt, aspha-min warm mix asphalt and SEAM warm mix asphalt are relatively large, showing a great dispersion degree of the tested results. (4) In comparison to the dry condition, the mean value of adhesion force in wet condition decreases by 47.2% for original base asphalt, by 22.0% for sasobit warm mix asphalt, by 11.9% for EC120 warm mix asphalt, by 13.3% for aspha-min warm mix asphalt and by 18.5% for SEAM warm mix asphalt. From the point of the view of the absolute value, under the wet condition, the adhesion strength of aspha-min warm mix asphalt and SEAM warm mix asphalt is stronger than that of other warm mix asphalts, which shows a better resistance ability to water damage. According to the relative value, EC120 warm mix asphalt and aspha-min warm mix asphalt have the lowest moisture sensitivity. The adhesion force between the asphalt binder and the mineral aggregate is hardly impacted by the change of the moisture conditions outside, which leads to a better
water-resistance ability. electrically neutral molecules in asphalt are The reasons are that: (1) the sasobit is a colliding or approaching the zeolite molecular kind of long chain aliphatic hydrocarbon particles, the Van der Waals' force inside the generated in the coal gasification process with asphalt system turns into relatively big the chain of carbon atoms ranging from C5 to attractive force, dramatically enhancing the C100. It is essentially the paraffin fine crystals, adhesion between the asphalt and the binder. mainly composed of -CH2 and -CH3. As it is (4) The SEMA is a kind of mixed additive insoluble in water, the lubrication action of composed of sulphur and auxiliaries, wax enhances the surface tension between the containing over 97% sulphur. Under the asphalt molecule and mineral aggregate under high-speed shearing of the colloid grinder, the wet condition, which largely reduces the very fine sulfur granules uniformly distribute adhesion between asphalt and aggregate. (2) inside the asphalt binders. Part of sulphur The EC120 is a kind of linear aliphatic forms the meshy structure in the asphalt, hydrocarbon, with strong hydrophobicity and which increases the high-temperature hydrophobic migration, which cannot dissolve performance of the asphalt binder but in water due to many non-polar groups. The decreases its viscosity, making the asphalt increase of the surface tension between the mixtures easily mix and stir, spread and EC120 molecule and the mineral aggregate compact, even at a low temperature. This part with the presence of water results in the of sulphur mainly acts as diluent. The other decrease of adhesion force, but the influence part of sulphur uniformly distributes inside the is limited. (3) The aspha-min is a kind of asphalt binders in the form of crystal so that it artificial zeolite, very fine white powder with can increase the strength and stability of the meshy silicate composite structures among asphalt binders, but this part of sulphur does which there is space to accommodate the not dissolve in the water. Under the wet cations, molecules and ion group, like Na+, condition, the sulphur in the asphalt not only 2+ Ca and H2O. The aspha-min contains about improves the surface tension but also absorbs 21% water. When the temperature is among the oil in the asphalt, which breaks the colloid balance structure of asphalt and reduces the 85 ～182 , the released moisture induces the bubble effect in the asphalt, and the adhesion force between the asphalt and volume of asphalt binder increase, which mineral aggregate. makes the mix and compaction of asphalt The Analysis of the Tested Results of mixture to be finished at relatively low Aging Asphalt Binders temperature. On the other sides, due to the good adsorbability, good thermostability, The adhesion forces for aging asphalt binders openness and numerous cavities, when the are given in Table 4. Table 4. Adhesion Force Test Results of Aging Asphalt Binders Aspha-min 70#A Base Sasobit Warm EC120 Warm SEAM Warm Warm Mix Asphalt Mix Asphalt Mix Asphalt Mix Asphalt Point Asphalt 1 2 3 4 5
Dry 47.3 52.4 58.9 55.3 42.5
Wet 28.7 21.5 22.6 30.6 19.8
Dry 51.3 48.5 37.9 39.6 44.1
Wet 34.5 29.6 25.9 24.3 33.6
Dry 46.9 42.1 44.6 43.5 49.8
Wet 38.9 36.5 43.6 45.3 46.2
Dry 82.9 94.1 92.3 81.7 83.6
Wet 92.4 89.8 107.6 102.3 105.3
Dry 77.5 76.9 88.3 87.2 82.5
Wet 68.3 69.9 60.7 59.3 55.9
6 7 8 9 10 Average (nN) Standard Deviation(nN) Percent Variation(%)
41.7 48.9 50.8 56.7 61.5 51.6
21.5 28.8 20.7 24.2 26.6 24.5
45.3 46.2 37.8 35.7 45.6 43.2
35.8 30.1 27.3 22.5 23.4 28.7
55.2 45.6 52.3 48.6 48.4 47.7
36.8 38.5 36.2 46.2 43.8 41.2
91.7 92.5 85.4 91.6 87.2 88.3
88.4 92.7 91.6 90.4 107.5 96.8
76.3 79.6 84.1 86.1 74.5 81.3
58.4 68.6 67.3 60.8 55.8 62.5
6.316
3.688
4.900
4.535
3.831 3.979
4.406
7.466
4.733
5.199
12.24
15.05
11.34
15.80
8.03
4.99
7.71
5.82
8.31
The AFM test results show that: (1) compared with the original asphalt binders, the adhesion force of aging asphalt binders under dry condition decreases with different extents, in the order of 70#A base asphalt （ 47.2% ） ＞ EC120 warm mix asphalt （ 32.5% ） ＞ SEAM warm mix asphalt （ 26.1% ） ＞ sasobit warm mix asphalt （ 22.0% ） ＞ aspha-min warm mix asphalt （ 16.3% ） , which means that the aging process greatly lowers the moisture erosion resistance ability of all asphalt binders, further impairing the water damage resistance ability. The base asphalt is more sensitive to moisture and more vulnerable to water damage, no matter it is under original state or aging state. Among the five kinds of asphalt binders, the aging aspha-min warm mix asphalt, with the least loss of adhesion force and the relatively small dispersion degree of the tested adhesion force, has the maximum water-damage resistance ability. (2) The adhesion force between the aging asphalt binder and mineral aggregate also decreases under wet condition, following the order: 70#A base asphalt （ 56.6% ） ＞ EC120 warm mix asphalt （ 33.9% ） ＞ sasobit warm mix asphalt （ 33.6% ） ＞ SEAM warm mix asphalt （ 30.3% ） ＞ aspha-min warm mix asphalt （ 20.5% ） . This suggests that the water damage resistance ability remarkably decreases after aging and the aspha-min warm mix asphalt has the smallest decline.
9.66
Conclusions （1）The AFM can be used to measure the surface characteristic of warm mix asphalt binders and the adhesion force between the asphalt and the mineral aggregate. The method of the preparation of samples and the test method adopted in this work are valid and feasible. （2）For the original and dry samples, the adhesion force ranks in the order of SEAM warm mix asphalt ＞ aspha-min warm mix asphalt＞70#A base asphalt＞ EC120 warm mix asphalt ＞ sasobit warm mix asphalt. Aspha-min warm mix asphalt and SEAM warm mix asphalt show better adhesive ability with the mineral aggregate in comparison to other asphalt binders, but their test results have relatively large dispersion and fluctuation. （3）With respect to the original and wet samples, aspha-min warm mix asphalt and SEAM warm mix asphalt show stronger water damage resistance ability; EC120 warm mix asphalt and aspha-min warm mix asphalt are less sensitive to moist and have stronger ability to resist water erosion, since the external moisture conditions change has very small influence on the adhesion force. （ 4 ） The aging process significantly reduces the moisture erosion resistance ability, which further impairs the water damage
resistance ability under the rank of 70#A base asphalt＞EC120 warm mix asphalt＞SEAM warm mix asphalt＞sasobit warm mix asphalt ＞aspha-min warm mix asphalt. （5）The base asphalt is more sensitive to moisture and more vulnerable to water damage, no matter whether it is under the original or aging state. （6）No matter it is dry or wet, the aging aspha-min warm mix asphalt has the least loss of adhesion force, the smallest dispersion of the tested adhesion force, the strongest water-damage resistance ability.
and Yoon, H. H. (1997). Investigation of the effect of aggregate pretreatment with anti-stripping agents on the asphalt-aggregate bond. Petroleum Science and Technology, 15(3-4), pp. 245-271. 5.
Wasiuddin, N. M., Zaman, M. M., O’Rear, E. A. (2008). Effect of sasobit and aspha-min on wettability and adhesion between asphalt binders and aggregates. Transportation Research Record: Journal of the Transportation Research Board, 2051, pp. 80-89.
6. Sadd, M. H., Dai, O., Parameswaran, V., and Shukla, A. (2003). Simulation of asphalt materials using a finite element micromechanical model with damage mechanics. Transportation Research
Acknowledgments
Record: Journal of the Transportation Research Board, 1832, pp. 86-95.
This research was funded by Scientific Research Project of Hunan Provincial Education Department No. 15B253, Natural Science Foundation of Hunan Province No. 2016JJ5009 and Research Learning and Innovative Experimental Project of Central South University of Forestry & Technology.
7. Hicks, R. G., Leahy, R. B., Cook, M., Moulthrop, J. S., and Button, J. (2004). Road map for mitigating national moisture sensitivity concern in hot mix pavements. 83rd Annual Meeting of Transportation Research Record, National Research Council, Washington, D.C. 8. Masad, E., Castelblanco, A., and Birgisson, B. (2006). Effects of air void size distribution, pore
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S1996-6814(16)30028-1 http://dx.doi.org/10.1016/j.ijprt.2016.11.001 IJPRT 52
To appear in:
International Journal of Pavement Research and Technology
Received Date: Accepted Date:
26 February 2016 3 November 2016
Please cite this article as: L. Kefei, D. Linfei, Z. Jiayu, Nanoscale Study on Water Damage for Different Warm Mix Asphalt Binders, International Journal of Pavement Research and Technology (2016), doi: http://dx.doi.org/ 10.1016/j.ijprt.2016.11.001
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Nanoscale Study on Water Damage for Different Warm Mix Asphalt Binders LIU Kefei1+ , DENG Linfei 1 and ZHENG Jiayu1 Abstract: In order to analyze the water damage to different warm mix asphalt binders from the the micro scale, five kinds of asphalt binders, 70#A base asphalt, sasobit warm mix asphalt, energy champion 120 （ EC120 ） warm mix asphalt, aspha-min warm mix asphalt, sulphur-extended asphalt modifier (SEAM) warm mix asphalt, under different conditions (dry/wet, original/aging) are prepared for laboratory tests. The atomic force microscope (AFM) is used to observe the surface properties and measure the adhesion force between the asphalt and the mineral aggregate. The obtained results show that under the dry condition aspha-min warm mix asphalt and SEAM warm mix asphalt show stronger adhesive ability with the mineral aggregate compared with other asphalt binders, but also have relatively large dispersion and fluctuation in the tested results; under the wet condition, aspha-min warm mix asphalt and SEAM warm mix asphalt show stronger water damage resistance ability. The EC120 warm mix asphalt and aspha-min warm mix asphalt are less sensitive to moist, and their corresponding adhesion force is less susceptible to the change of external moisture conditions, leading to a better ability to resist water erosion. The aging process significantly lowers the moisture erosion resistance ability, which further impairs the water damage resistance ability. The base asphalt is more sensitive to moisture and more vulnerable to water damage, no matter whether it is under original or aging conditions. The aging aspha-min warm mix asphalt has the least loss of adhesion force, the smallest dispersion of the tested adhesion force, the strongest water damage resistance ability, no matter it is dry or wet. Key words: Road engineering; Warm mix asphalt; Moisture damage; Atomic force microscope; Microcosmic pavement have not been solved thoroughly: 1 Introduction How to exactly measure the asphalt mixture performance loss caused by moisture variation? The material and structural characteristic of How to effectively reduce the water damage to asphalt concrete pavement make it more asphalt pavement? susceptible to the moisture condition. The Numerous studies [1-6] have showed that decrease of the adhesion force causes the the water damage of asphalt binders (mixtures) water damage at the asphalt-aggregate occurs at the molecular scale, or even at the interface. Although the domestic and overseas nanometer scale. This is because of the fact researches on water damage to asphalt that the root cause of water damage to asphalt pavement has lasted nearly 70 years, this binders is related to the loss of the adhesion problem has not yet been effectively addressed. force and the cohesion force. The loss of the Two key problems of water damage in asphalt adhesion force refers to the decline of the adhesive ability at the asphalt-aggregate 1 Associate Professor, College of Civil interface as a result of the water and water Engineering and Mechanics, Central South pressure acting on the asphalt mixture; the loss University of Forestry & Technology, of the cohesion force is due to the softening or China-410004. + the impairment of cohesion capability inside Corresponding Author: E-mail [email protected]
the asphalt binder subjected to the moisture and seepage force. Both the adhesion force loss and the cohesion force loss happen at the nanometer scale. Therefore, to quantify the adhesion force or the cohesion force at the nanometer scale is of highly positive practical significance to the research and prevention of water damage to the asphalt pavement. The microscopic researches on water damage to the asphalt binders at home and aboard mainly focus on base asphalt and SB/SBS modified asphalt. However, there are few reports about the investigation of warm mix asphalt at the nanometer scale. With the application of the high-definition 3D image resolution of the atomic force microscope (AFM) and a precise force-displacement measurement system, the adhesion force between the asphalt-aggregate molecules is analyzed for different asphalt binders under dry/wet, original/aging states at the laboratory, followed by the evaluation of the water damage resistance for each warm mix asphalt binder under different conditions. The research results can provide theoretical basis for the discovery of the mechanism of water damage and the reduction of water damage. It should be noted that parallel tests are conducted in this article using modified asphalt SBS as comparative material, and the results showed no visible difference. In consequence, this article only presented the effects of base asphalt and warm mix modifies on water damage of asphalt binder.
Review of Previous Studies Research on water damage of asphalt binder & mixture dates back to the 1930s, from asphalt to mineral aggregate, from test methodology to pavement structure[7]. To date, numerous test
methods have been developed and used to predict moisture-induced damage in asphalt concrete[8-10]. In the past two decades, there
have been significant improvements in moisture damage test methods and our understanding of the microscale to macroscale behavior of asphalt concrete. There exists evidence that moisture-induced damage in asphalt concrete is influenced by factors such as asphalt grade, viscosity, modifiers, phenol group concentrations, aggregate surface chemistry, minerals, roughness, porosity, clay coatings, mix air voids, asphalt content, permeability, and binder thickness. Yet, a combination of asphalt and aggregate that would be compatible enough to produce moisture damage-free asphalt concrete is not available[11]. There is an urgent need for the development and assessment of testing methods capable of examining the effect of moisture on asphalt concrete. Moisture damage within the binder and/or at asphalt-aggregate interfaces has been studied by several researchers[2,6,8]. Recently, the surface free energy of asphalt and aggregate has been empirically related to the moisture-induced damage of asphalt concrete[2,5]. The surface free energy of asphalt and aggregate is indirectly measured using the Wilhelmy plate, sorption device, and Youn-Dupré equation. However, the Wilhelmy plate method cannot differentiate between the functional groups. For example, the surface free method fails to differentiate between actions of carboxylic acid (bad) and carbonyls (good), or carboxylic acid (bad) and nitrogen compound (good) under wet conditions. Also, the Wilhelmy plate technique cannot clearly distinguish between untreated asphalt and asphalt treated with amine antistrip. By the same token, the universal sorption device requires vacuum degas preconditioning, which is very different from the mixing plant conditions. More recently, Rafiqul et al [12] tested the adhesion forces between base asphalt as well as SB & SBS modified asphalts and different functional probes. The results
showed that modifiers SB and SBS can improve the water damage-proof ability of base asphalt and a 3% SB & SBS dosage can obtain the best effect. In addition, critical parameters for AFM testing on modified asphalt were also confirmed basically.
Material and Test Method Raw Materials The raw materials used in the tests include: (1) The base asphalt: 70#A pavement petroleum asphalt. (2) The warm mix modifier sasobit: with low melting point and organic viscosity-reducing character. The admixture dosage is 3.0 percent of the mass of the asphalt binder, which can lower the mixed and compacted temperature by 20 ～ 30 . (3) The warm mix additive energy champion 120 (EC120): a kind of linear aliphatic hydrocarbons. The admixture dosage is 3.0 percent of the mass of the asphalt binder, lowering the mixed and compacted temperature by 20 ～30 . (4) The warm mix additive aspha-min: the artificial synthetic white powder zeolite. The admixture dosage is 0.3 percent of the mass of the asphalt binder, lowering the mixed and compacted temperature by 10 ～25 . (5) The warm mix additive sulphur-extended asphalt modifier (SEAM): the sulfur. The admixture dosage is 30 percent of the mass of the asphalt binder, lowering the mixed and compacted temperature by 20 ～35 . Each appearance of warm mix additives is shown in Figure 1, and the main technical parameters of the asphalt binders are listed in Table 1.
The Preparation of Samples In order to ensure the AFM to reliably observe the nanometer-scale surface properties of asphalt binders, the one-blending method is
used to prepare the warm mix asphalt samples which are theoretically finely dispersed and uniformly distributed. In order to make the binder surface smooth, the particle size of asphalt mortar should be as small as possible, an advanced colloid mill machine (2000 mesh) is taken to grind the warm mix asphalt fully mixing the warm agents with the asphalt, at the revolving speed 4500rpm and grinding time 4h. The detailed preparation technology is sketched in Figure 2. Moreover, size of material will not change the character of itself and the usage of colloid mill machine for asphalt binder grinding will also make no difference to the results or the engineering application. In order to compare the adhesion forces between asphalt and aggregate molecules under different conditions, according to the test code of ASTM D6521, the original and aging samples are obtained by further processed the residuary asphalts with PAV stress aging（100 ）which are left after the RTFOT（163 ） aging. The basic technical parameters for aging asphalt binders are given in Table 1. In order to prevent the further aging, firstly respectively place 20g of the prepared asphalt binders into an oven at 140 and rapidly heat to melt; then drip moderate melted binders on a glass slide and put the glass slide into an oven at 140 for five minutes to obtain a smooth surface; finally take out the sample and keep it natural cooling to room temperature.
(a) Sasobit
(b) EC120
(c) Aspha-min
(d) SEAM
Fig.1. The Appearance of Warm Mix Additives Table 1. Main Technical Indexes of Each Asphalt Binder Type of Asphalt
70#A Base Asphalt
Sasobit Warm Mix Asphalt
EC120 Warm Mix Asphalt Aspha-min Warm Mix Asphalt SEAM Warm Mix Asphalt
Original After PAV Aging Original After PAV Aging Original After PAV Aging Original After PAV Aging Original After PAV
Penetration (25℃)(0.1mm)
Penetration Index PI
Ductility (5℃)(cm)
Softening Point(℃)
76
-0.80
19
46.4
Elastic Recovery (25℃) (%) --
52
-0.68
9.8
52.4
--
56
0.37
14.8
63.5
89.1
48
0.43
11.0
73.0
82.6
59
0.46
12.7
61.7
87.4
51
0.51
9.8
68.5
81.6
61
0.39
17.9
58.2
89.6
53
0.45
12.9
64.3
83.7
63
0.40
13.5
64.1
91.0
54
0.47
8.3
70.4
82.3
Aging
Fig.2. Preparation Process Flow Chart for Warm Mix Asphalt Binder For the purpose of comparisons between force-displacement curves. The scanned the dry and wet conditions, making reference figures were further processed using the to Reference [12], the wet samples were MATLAB. Ten feature points were scanneded obtained by firstly putting the dry samples in a for each sample, and the mean value of these vacuum dryer to evacuate to full vacuum and ten points was taken as the measured adhesion then immersing them in water for 72h. We force. obtained totally 20 kinds of original/aging and dry/wet asphalt binders. The Analysis of the AFM Images Before the AFM tests, all samples were placed into an oven at 140 for 2 hours for of Asphalt Binders desiccated surfaces. The typical micrographs and stereographs for Method of AFM Tests asphalt binders are shown in Figure 3. Only The Digital Instruments-Veeco Metrology the figures of the dry samples are provided for Group AFM with image resolution 180 x 180 the sake of the space. According to the points and maximum scanning range 15µm× working principle of AFM and the 15µm is used to perform all tests at the requirement of test accuracy[13-15], the mean tapping mode. The resonance frequency of value, maximum value and root-mean-square micro-cantilever is 260 kHz. of the surface roughness for each asphalt In order to effectively simulate the binder were calculated and listed in Table 2. measurement of asphalt-aggregate adhesion As seen in Table 2, the maximum and force, the silicon nitride (Si3N4) probe is used minimum values of surface roughness RMS to get the three-dimensional images at the are, respectively, 32.46nm and 7.71nm. These asphalt binder surface and measure the measured values agree well with the advice adhesion force, under the scanning frequency for the measurement of surface roughness of of 3Hz, as Silicon is the basic elements of viscoelastic material using AFM, which verify rocks and minerals. During the experiments, the preparation of the samples and the the testing work mainly focused on, with the experimental method adopted in this article. application of the probe, the search of the feature points at the surface of samples, the scan of the image, the measurement of the
（a1）Micrograph of 70#A Base Asphalt
（a2）Stereogram of 70#A Base Asphalt
(b1) Micrograph of Sasobit Warm Mix Asphalt
(b2) Stereogram of Sasobit Warm Mix Asphalt
(c1) Micrograph of EC120 Warm Mix Asphalt
(c2) Stereogram of EC120 Warm Mix Asphalt
(d1) Micrograph of Aspha-min Warm Mix Asphalt
(d2) Stereogram of Aspha-min Warm Mix Asphalt
(e1) Micrograph of SEAM Warm Mix Asphalt
(e2) Stereogram of SEAM Warm Mix Asphalt
Fig.3. Typical Surface Images of Each Asphalt Binder (Dry Sample) Table 2. Roughness Calculation Results of Each Asphalt Binder Dry Average Maximum Root-Mean Average Type of Asphalt Value Value -Square Value (nm) (nm) (nm) (nm) Original 9.3 20.2 12.51 11.3 70#A Base After Asphalt PAV 11.7 24.3 14.77 14.6 Aging Original 9.9 19.8 13.13 12.5 Sasobit After Warm Mix PAV 12.1 17.6 15.32 14.5 Asphalt Aging Original 6.5 9.6 7.71 8.3 EC120 After Warm Mix PAV 8.9 12.1 9.54 11.2 Asphalt Aging Original 21.2 41.7 24.11 24.3 Aspha-min After Warm Mix PAV 23.7 45.9 27.86 28.9 Asphalt Aging Original 24.1 44.6 28.35 27.3 SEAM After Warm Mix PAV 28.3 48.5 29.97 30.1 Asphalt Aging
Besides, both the obtained micrographs and stereographs can visually reflect the degree of surface evenness (or surface roughness) of these samples. Among the five samples, the surface morphology of 70#A base asphalt is relatively smooth, since it has no any additives. Even though there are some slight pits in the 70#A base asphalt, their distributions are relatively uniform. Under the effect of the high-speed shearing of colloid
Wet Maximum Value (nm) 24.9
Root-Mean -Square (nm) 14.18
26.3
16.22
24.6
14.27
26.9
17.73
14.2
8.85
18.3
12.16
46.2
28.56
48.8
31.12
49.4
30.52
48.9
32.46
grinder, a uniform and stable spatial network system is generated in the sasobit warm mix asphalt or the EC120 warm mix asphalt in which several relatively large polymer particles exist, but both two kinds of warm mix additives basically disperse well among the base asphalts, the surface morphology of the binders being relatively smooth and even, which constitutes a good compatible system. The surfaces of aspha-min warm mix asphalt and SEAM warm mix asphalt are very rough
with many sags and crests under irregular distributions. The maximum height in Z-axis is about 50 nm. This indicates that the addition of warm mix additives aspha-min and SEAM into the base asphalt significantly increases the granular size and dispersion degree of the mixed particles, thus the compatibility is poorer than those of other warm mix binders[16].
The Measurement of Adhesion Force
The force-distance curves of the dry original samples for all warm mix asphalts are shown in Figure 4. The horizontal axis in Figure 4 represents the distance between the Si3 N4 probe and the sample surface, and the vertical axis represents the magnitude of the force between the probe molecule and the asphalt molecule, positive values for repulsive forces and negative values for attractive forces. Each test cycle starts at the position with a distance bigger than 500nm from the sample surface. The curves in Figure 4 show that there are four representative sections, respectively separated by points A, B, C and D.
(a) 70#A Base Asphalt
(b) Sasobit Warm Mix Asphalt
(c) EC120 Warm Mix Asphalt
(d) Aspha-min Warm Mix Asphalt
(e) SEAM Warm Mix Asphalt
Fig.4. Force-distance Test Chart of Each Asphalt Binder (Dry Sample) When the probe is far away from the sample surface (the right part at point A on the curve), there is no interaction between the probe molecule and the asphalt molecule. As the probe is approaching the sample surface, the attractive force between the probe molecule and asphalt molecule makes the
probe further move close to the sample (the AB part on the curve). This attractive force reaches its maximum value at point B beyond which point the attractive force gradually turns into the repulsive force which stops the probe approaching. The closer the probe gets to the surface of sample, the faster the
repulsive force grows (the BC part on the curve). The repulsive force reaches its peak at point C when the probe molecule gets infinitely close to the asphalt molecule. Then, the probe begins to get away from the sample surface. At the beginning, the attractive force dominates the interaction between the probe molecule and asphalt molecule, and this attractive force increases with the increase of the distance between these two molecules (the CD part on the curve), reaching the maximum value at point D. After point D, the probe molecule gets rid of the restriction of adhesion force from the asphalt molecule and slowly returns to the initial state (the DA part on the
curve). The corresponding value at point D represents the maximum adhesion force between the probe and asphalt molecules caused by the van der waals’ force [17, 18].
The Analysis of the Tested Results The Analysis of the Tested Results of Original Asphalt Binders The tested adhesion forces for original asphalt binders are given in Table 3.
Table 3.
Adhesion Force Test Results of Original Asphalt Binders Sasobit Aspha-min 70#A Base EC120 Warm Warm Mix Warm Mix Asphalt Mix Asphalt Point Asphalt Asphalt Dry Wet Dry Wet Dry Wet Dry Wet 71.3
67.5
67.9 68.5
69.4 55.6
77.4
57.9
73.5 70.1 69.0
63.1 67.3 56.6
66.4 72.2
55.8 68.3
70.8 70.7
61.5 62.3
3.82 4
2.99 6
8.85
4.24
1
103.7
71.3
49.6
38.5
2
88.9
52.5
52.7
42.7
3
111.2
47.9
58.8
46.8
4
101.5
50.7
59.1
44.3
5 6
86.5 88.2
58.5 47.8
54.3 55.6
39.6 37.2
7
107.4
46.7
56.1
45.8
8
85.3
63.4
52.5
47.5
9
91.2
67.9
58.4
40.9
10
114.1
57.3
56.9
48.7
Average (nN)
97.8
56.4
55.4
43.2
10.41 5
8.34 6
2.95 9
10.42
14.8 0
5.34
Standard Deviation(nN ) Percent Variation(%)
Combined with the previous research, the
97.9 95.4 103. 8 96.9 109. 3 119.8 105. 5
125. 4 119.6 132. 7 121. 5 118.3 119.0 125. 7 116.4 121. 0 117.5 121. 7
5.27 9
8.42 5
8.47
7.99
117.4 113.1 102. 8 98.6
SEAM Warm Mix Asphalt Dry 98.7 117.4 105.9 93.5 102.6 95.5 93.9 112.6 96.2
Wet 84.6 88.2 95.7 99.6 80.3 83.1 101. 5 87.6 92.5
103.6
83.9
110.0
89.7
4.69 3
11.10 8
6.92 3
3.86
10.10
7.72
process of water infiltration in asphalt binder
is known as follows: hydrone has a tremendous polarity, and once water contacted with the asphalt surface, the interaction between hydrones and the polar molecules or groups such as aromatic hydrocarbons, colloids and asphaltenes in asphalt will take place by orientation forces, and a micro-activating center will then formed by hydrones aggregation. Due to the directionlessness and saturability of orientation forces, the adsorbed hydrones will continue to interact with the polar groups nearby to form new micro-activating centers. Similarly, the micro-activating centers can also be formed through the induction forces between the hydrones and the nonpolar molecules & constituents, what’s more, due to the directionlessness and saturability of the induction forces, just like the orientation forces, the hydrones will also continue to interact with the nonpolar constituents nearby. In addition, the hydrones will interact with the oxygen and nitrogen atoms in asphalt to form hydrogen bonds. Capillary channels for water enrichment and infiltrate constructed by micro-activating centers are formed by the above three types of intermolecular interactions, through these channels, water enriches in the asphalt layer and expand to the mineral aggregate surface. This is how the progress of water diffusion passage formed. After it, hydrones continually get to reach the interface of the asphalt and mineral aggregates and interact with the asphalt as mentioned above. More hydrones get into the asphalt as the contact surface getting large and then the asphalt will get saturated and accommodates no hydrones any more when the interactions between hydrones and polar and nonpolar component & strong electronegativity elements were completed. In the progress, a slower capillary channels formation velocity means a smaller velocity of water diffusion, namely a greater capacity of water
damage-proof and vice versa. Based on the above analysis, conclusions from the AFM tests can be drawn: (1) the most gentle curve near point D comes from the original base asphalt in the Figure 4, which indicates that its viscosity is obviously greater than that of the warm mix asphalts. This is consistent with the previous studies. (2) For the original asphalt binders, the ranking order of the adhesion force under dry condition is: SEAM warm mix asphalt （ 110.0nN ） ＞ aspha-min warm mix asphalt（105.5nN）＞ 70#A base asphalt（97.8nN）＞EC120 warm mix asphalt（70.7nN）＞sasobit warm mix asphalt (55.4nN). This means that under the dry condition the aspha-min warm mix asphalt and SEAM warm mix asphalt have better adhesion to the mineral aggregate than that of other asphalt binders. (3) Under the dry condition, the standard deviation of the tested adhesion force for original base asphalt, aspha-min warm mix asphalt and SEAM warm mix asphalt are relatively large, showing a great dispersion degree of the tested results. (4) In comparison to the dry condition, the mean value of adhesion force in wet condition decreases by 47.2% for original base asphalt, by 22.0% for sasobit warm mix asphalt, by 11.9% for EC120 warm mix asphalt, by 13.3% for aspha-min warm mix asphalt and by 18.5% for SEAM warm mix asphalt. From the point of the view of the absolute value, under the wet condition, the adhesion strength of aspha-min warm mix asphalt and SEAM warm mix asphalt is stronger than that of other warm mix asphalts, which shows a better resistance ability to water damage. According to the relative value, EC120 warm mix asphalt and aspha-min warm mix asphalt have the lowest moisture sensitivity. The adhesion force between the asphalt binder and the mineral aggregate is hardly impacted by the change of the moisture conditions outside, which leads to a better
water-resistance ability. electrically neutral molecules in asphalt are The reasons are that: (1) the sasobit is a colliding or approaching the zeolite molecular kind of long chain aliphatic hydrocarbon particles, the Van der Waals' force inside the generated in the coal gasification process with asphalt system turns into relatively big the chain of carbon atoms ranging from C5 to attractive force, dramatically enhancing the C100. It is essentially the paraffin fine crystals, adhesion between the asphalt and the binder. mainly composed of -CH2 and -CH3. As it is (4) The SEMA is a kind of mixed additive insoluble in water, the lubrication action of composed of sulphur and auxiliaries, wax enhances the surface tension between the containing over 97% sulphur. Under the asphalt molecule and mineral aggregate under high-speed shearing of the colloid grinder, the wet condition, which largely reduces the very fine sulfur granules uniformly distribute adhesion between asphalt and aggregate. (2) inside the asphalt binders. Part of sulphur The EC120 is a kind of linear aliphatic forms the meshy structure in the asphalt, hydrocarbon, with strong hydrophobicity and which increases the high-temperature hydrophobic migration, which cannot dissolve performance of the asphalt binder but in water due to many non-polar groups. The decreases its viscosity, making the asphalt increase of the surface tension between the mixtures easily mix and stir, spread and EC120 molecule and the mineral aggregate compact, even at a low temperature. This part with the presence of water results in the of sulphur mainly acts as diluent. The other decrease of adhesion force, but the influence part of sulphur uniformly distributes inside the is limited. (3) The aspha-min is a kind of asphalt binders in the form of crystal so that it artificial zeolite, very fine white powder with can increase the strength and stability of the meshy silicate composite structures among asphalt binders, but this part of sulphur does which there is space to accommodate the not dissolve in the water. Under the wet cations, molecules and ion group, like Na+, condition, the sulphur in the asphalt not only 2+ Ca and H2O. The aspha-min contains about improves the surface tension but also absorbs 21% water. When the temperature is among the oil in the asphalt, which breaks the colloid balance structure of asphalt and reduces the 85 ～182 , the released moisture induces the bubble effect in the asphalt, and the adhesion force between the asphalt and volume of asphalt binder increase, which mineral aggregate. makes the mix and compaction of asphalt The Analysis of the Tested Results of mixture to be finished at relatively low Aging Asphalt Binders temperature. On the other sides, due to the good adsorbability, good thermostability, The adhesion forces for aging asphalt binders openness and numerous cavities, when the are given in Table 4. Table 4. Adhesion Force Test Results of Aging Asphalt Binders Aspha-min 70#A Base Sasobit Warm EC120 Warm SEAM Warm Warm Mix Asphalt Mix Asphalt Mix Asphalt Mix Asphalt Point Asphalt 1 2 3 4 5
Dry 47.3 52.4 58.9 55.3 42.5
Wet 28.7 21.5 22.6 30.6 19.8
Dry 51.3 48.5 37.9 39.6 44.1
Wet 34.5 29.6 25.9 24.3 33.6
Dry 46.9 42.1 44.6 43.5 49.8
Wet 38.9 36.5 43.6 45.3 46.2
Dry 82.9 94.1 92.3 81.7 83.6
Wet 92.4 89.8 107.6 102.3 105.3
Dry 77.5 76.9 88.3 87.2 82.5
Wet 68.3 69.9 60.7 59.3 55.9
6 7 8 9 10 Average (nN) Standard Deviation(nN) Percent Variation(%)
41.7 48.9 50.8 56.7 61.5 51.6
21.5 28.8 20.7 24.2 26.6 24.5
45.3 46.2 37.8 35.7 45.6 43.2
35.8 30.1 27.3 22.5 23.4 28.7
55.2 45.6 52.3 48.6 48.4 47.7
36.8 38.5 36.2 46.2 43.8 41.2
91.7 92.5 85.4 91.6 87.2 88.3
88.4 92.7 91.6 90.4 107.5 96.8
76.3 79.6 84.1 86.1 74.5 81.3
58.4 68.6 67.3 60.8 55.8 62.5
6.316
3.688
4.900
4.535
3.831 3.979
4.406
7.466
4.733
5.199
12.24
15.05
11.34
15.80
8.03
4.99
7.71
5.82
8.31
The AFM test results show that: (1) compared with the original asphalt binders, the adhesion force of aging asphalt binders under dry condition decreases with different extents, in the order of 70#A base asphalt （ 47.2% ） ＞ EC120 warm mix asphalt （ 32.5% ） ＞ SEAM warm mix asphalt （ 26.1% ） ＞ sasobit warm mix asphalt （ 22.0% ） ＞ aspha-min warm mix asphalt （ 16.3% ） , which means that the aging process greatly lowers the moisture erosion resistance ability of all asphalt binders, further impairing the water damage resistance ability. The base asphalt is more sensitive to moisture and more vulnerable to water damage, no matter it is under original state or aging state. Among the five kinds of asphalt binders, the aging aspha-min warm mix asphalt, with the least loss of adhesion force and the relatively small dispersion degree of the tested adhesion force, has the maximum water-damage resistance ability. (2) The adhesion force between the aging asphalt binder and mineral aggregate also decreases under wet condition, following the order: 70#A base asphalt （ 56.6% ） ＞ EC120 warm mix asphalt （ 33.9% ） ＞ sasobit warm mix asphalt （ 33.6% ） ＞ SEAM warm mix asphalt （ 30.3% ） ＞ aspha-min warm mix asphalt （ 20.5% ） . This suggests that the water damage resistance ability remarkably decreases after aging and the aspha-min warm mix asphalt has the smallest decline.
9.66
Conclusions （1）The AFM can be used to measure the surface characteristic of warm mix asphalt binders and the adhesion force between the asphalt and the mineral aggregate. The method of the preparation of samples and the test method adopted in this work are valid and feasible. （2）For the original and dry samples, the adhesion force ranks in the order of SEAM warm mix asphalt ＞ aspha-min warm mix asphalt＞70#A base asphalt＞ EC120 warm mix asphalt ＞ sasobit warm mix asphalt. Aspha-min warm mix asphalt and SEAM warm mix asphalt show better adhesive ability with the mineral aggregate in comparison to other asphalt binders, but their test results have relatively large dispersion and fluctuation. （3）With respect to the original and wet samples, aspha-min warm mix asphalt and SEAM warm mix asphalt show stronger water damage resistance ability; EC120 warm mix asphalt and aspha-min warm mix asphalt are less sensitive to moist and have stronger ability to resist water erosion, since the external moisture conditions change has very small influence on the adhesion force. （ 4 ） The aging process significantly reduces the moisture erosion resistance ability, which further impairs the water damage
resistance ability under the rank of 70#A base asphalt＞EC120 warm mix asphalt＞SEAM warm mix asphalt＞sasobit warm mix asphalt ＞aspha-min warm mix asphalt. （5）The base asphalt is more sensitive to moisture and more vulnerable to water damage, no matter whether it is under the original or aging state. （6）No matter it is dry or wet, the aging aspha-min warm mix asphalt has the least loss of adhesion force, the smallest dispersion of the tested adhesion force, the strongest water-damage resistance ability.
and Yoon, H. H. (1997). Investigation of the effect of aggregate pretreatment with anti-stripping agents on the asphalt-aggregate bond. Petroleum Science and Technology, 15(3-4), pp. 245-271. 5.
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Acknowledgments
Record: Journal of the Transportation Research Board, 1832, pp. 86-95.
This research was funded by Scientific Research Project of Hunan Provincial Education Department No. 15B253, Natural Science Foundation of Hunan Province No. 2016JJ5009 and Research Learning and Innovative Experimental Project of Central South University of Forestry & Technology.
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